Just a little help to keep you from straying off on the wrong path...
I bought my truck from some random guy at craigslist and what i didn't know was that there was no oxygen sensor. Took me a while to figure out why i was getting such crappy mpg but when I got around to looking for it I found a bolt in place of the oxygen sensor. Long story short, my truck (93 f150 5.0L) ran great without it before and the only noticeable effect now of having the O2 sensor is better mpg. Could be a black magic O2 sensor problem for you but for me, not having one barely affected my truck.